Portable electric tool equipped with a device that can be used to determine the relative position of two elements of said tool at least one of which is movable

ABSTRACT

Portable electric tool including a body configured to act as a handgrip and at one of the ends of which there is mounted a moving active member, the movements of which are brought about by an actuator, characterized in that the moving part is equipped with an oriented magnetization magnet that can be moved past a magneto-resistive sensor fixed to a fixed element of the body. The trigger is equipped with an oriented magnetization magnet that can be moved past a magneto-resistive sensor fixed to a fixed element of the body. The portable electric tool further includes an electronic board for analyzing the information emitted by each magneto-resistive sensor according to the inclination of the magnetic field lines presented to it, in order to control the operation of the actuator so as to position the moving part accurately according to the position of the control device.

CROSS-REFERENCE TO RELATED U.S. APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

REFERENCE TO AN APPENDIX SUBMITTED ON COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a portable electric tool equipped with adevice that can be used to precisely determine, continuously and withoutcontact, the relative position between two cooperating parts of twocooperating elements of said tool, at least one of which is linearly orangularly movable. It can be applied to portable electric tools and, inparticular, although not exclusively, to electronic pruning shears orsimilar tools that have cutting blades whose closure is controllable.

2. Description of Related Art Including Information Disclosed Under 37CFR 1.97 and 37 CFR 1.98

Most frequently, in devices that involve the linear or angular travel ofa movable element according to a user-defined order, we find twocooperating elements such as, in the case of portable electric tools: acontrol that gives the order and may consist of a trigger; and anactuator that carries out the action and may be connected to the motorby a transmission system.

The connection between the control and the actuator is electronicallyprovided by a control board having a microprocessor and that must alsomeasure the linear or angular travel of the actuator to ensure that thecontrol order has in fact been carried out.

Currently, there exist a variety of devices that can be used to fulfillthis function, having their inherent advantages and, especially, theirinherent disadvantages.

For example, we know of systems of potentiometric linear or angularsensors used to measure travel through a change in the value of theirresistance, this change being linear and processed by an electroniccontrol board. The principal drawbacks of these potentiometric linear orangular sensors are the presence of two parts in contact, which slideagainst one another, each of which is affixed to one of the movingparts; the length of these devices being equal in length to the travel(linear or angular), they take up space, and their wear, associated withtheir friction, results in changing precision over time and a relativelyshort lifecycle.

To avoid contact between the moving parts, systems exist that make useof Hall-effect sensors C1, C2, C3, C4, C5, mounted successively on thefixed part and a radially magnetized magnet affixed to the moving part,the Hall-effect sensors issuing a signal whenever they are presentedwith a magnetic field.

The drawbacks of this solution, illustrated in FIG. 1, include thenecessity of using a large number of costly sensors and, especially, inthat it cannot be used to accurately determine the position of themoving part between two sensors, resulting in low precision. The totaltravel L being the sum of the travels l1+l2+l3+l4, the precision is thusthat of the travel between two sensors. It is impossible to determine arandom travel position with precision without having an infinite numberof sensors, which is physically impossible.

Systems are also known that make use of a magnetoresistive sensor (aparticularity of which is that it measures the inclination of fieldlines in a magnetic field) together with a radially magnetized magnet(magnetization is perpendicular to the magnet).

This solution, illustrated in FIG. 2, has the advantage of being simpleand contact free, but it has the disadvantage of lacking precision andrequires a considerable distance between sensor and magnet, especiallywhen travel is significant. In this diagram we find that for a giventravel, one can measure, at the end of travel, an angle of 45° of themagnet's field line, the distance between the magnet and the sensor “l”must therefore be L/2. Consequently, as the travel increases, distance“l” increases. Additionally, the greater the distance, the stronger themagnet's magnetic field must be in order to be detected by the sensor.

We also know (DE-19612422, EP-0997706, EP-1074818, FR-2898189) of adevice for determining the relative position between two cooperatingparts at least one of which is linearly movable, one of these partsbeing equipped with a magnet whose magnetization is oriented, whereasthe other part is equipped with a magneto-resistive sensor, wherein theanalog electrical information emitted by the magneto-resistive sensorcan be analyzed based on the inclination of the magnetic field linespresented to it in order to determine the relative position between thetwo parts with precision.

The invention concerns the integration of such devices in portableelectric tools and, more specifically, in electric pruning shears orsimilar cutting tools in which it is advantageous to precisely determineand control, continuously and without the contact of mechanicalelements, the direction of movement and the position of at least twocooperating parts of such tools.

In a manner known per se, these electric pruning shears have at leastone movable cutting blade mounted at the anterior extremity of a bodyshaped to serve as a handgrip and within which is lodged an electricgear motor whose output is connected to said movable blade by means of amoving drive part or actuator, and a pivoting trigger accessible fromthe exterior of the body capable of activating an electrical controldevice.

It is known that into such tools can be integrated devices forcontrolling, with more or less precision, the position of the bladeactuator and, consequently, that of said blade, when the latter isopened and closed, based on the control order given by the user by meansof the trigger, so that the movement of said blade is dependent on themovement of said trigger, with a concern for the precision of the cut,comfort, and safety.

In FR-2614568 a description is given of a servocontrolled portableelectric tool in position wherein the moving part driving the pivotingblade consists of the ball assembly of a ball bearing ball screw systemthat can be driven axially in one direction or the other depending onthe direction of rotation of the screw, wherein the pivoting triggerused to actuate the electric control device is slaved to said ball whoselinear displacements it consequently follows. These rectilineartrajectories of the trigger limit the ball's length of travel to thelength of the user's finger. Moreover, because the electric controldevice moves together with the ball, it is necessary to link saidassembly and the connector by means of a flexible link or flexiblecircuit, such that wear on this flexible circuit may lead tomalfunctions.

In FR-2770372 different embodiments of a mechanically activated portablecutting tool are described, wherein the position of the movable cuttingblade is detected by various devices that make use of one or morepotentiometers, some linear and some rotary, or even through the use ofa mixed linear and rotary potentiometer device. We note that in allthese cases each potentiometer must be linked, on the one hand, to amoving part and, on the other hand, to the fixed body of the tool bymeans of oblong grooves for proper operation: in order to transformcertain rotational movements into linear movements and due to the factthat the centers of rotation are not necessarily the same for the movingpart and the potentiometer in the case of rotary potentiometers. Theprincipal drawback of these devices is that the presence of functionalplay at the oblong grooves is essential and, consequently, this playnecessarily introduces an error in the value of the position transmittedby the potentiometers, this error increasing with operational wear.Other drawbacks follow from the fact that the potentiometers arecomponents that have two tracks in permanent contact that wear quicklyif a large number of maneuvers are carried out; additionally, suchcomponents are costly and bulky.

WO-2005/084416 describes a mechanically activated cutting tool in whichthe movable cutting blade is detected by a plurality of Hall-effectsensors distributed along the arc of a circle on a fixed element of thetool body so as to enable the detection of the angular movements of amagnet affixed to an element integral with said pivoting cutting blade.The disadvantage of this device is that it cannot determine with highprecision the position of the pivoting cutting blade (the precision isequal to the angle between the two sensors) and is expensive given theneed to use a plurality of costly Hall-effect sensors.

Another object of the invention is to provide users with electricpruning shears that are free from the previously described drawbacks ofknown electric cutting tools and that can be used to provide greaterprecision and speed during cutting activities, as well as greater safetyfor users, by very precisely linking the open position of the blade tothe position of the trigger controlled by the user.

BRIEF SUMMARY OF THE INVENTION

The electric pruning shears to which the invention is applicable have atleast one movable active element at the anterior extremity of a bodyshaped to serve as a handgrip and within which is lodged an electricgear motor whose output is connected to said movable active element bymeans of a transmission system. These electric pruning shears furtherinclude a pivoting trigger accessible on the exterior of the body and anelectronic control device activated by the latter, connected to theelectronic control board of the gear motor.

The portable electric tool according to the invention notably compriseson the one hand, an actuator having two cooperating parts at least oneof which is linearly or angularly movable, the movable part of thisactuator being responsible for the movements of said movable element. Onthe other hand, a control device is used to control the operation of theactuator, this device comprising two cooperating parts at least one ofwhich is linearly or angularly movable This portable electric tool isespecially noteworthy in that one of the cooperating parts of saidactuator and said control device is equipped with a magnet whosemagnetization is oriented, while the other part is equipped with amagneto-resistive sensor;

Said portable electric tool further having an electronic control andmanagement board comprising a microprocessor, this electronic boardbeing configured to analyze the analog or digital electrical informationtransmitted by each magneto-resistive sensor depending on theinclination of the magnetic field lines presented to it, in order tocontrol the operation of the actuator and precisely position the movableelement based on the position of the control device.

More specifically, on the one hand, a magneto-resistive sensor isfixedly mounted on an element of the body or on an element integral tothe body, and the trigger, preferably the free extremity thereof, isequipped with a magnet whose magnetic field lines are oriented, whichcan be moved with respect to said magneto-resistive sensor by pivotingsaid trigger. On the other hand, a magneto-resistive sensor is fixedlymounted to the body of the tool and a magnet having oriented magneticfield lines is integrated with the movable ball of the ball bearing ballscrew system, and this oriented-magnetic-field-line magnet can be movedwith respect to said magneto-resistive sensor by the activation of saidball screw system.

It should be pointed out that the ball screw system can have a movableball and rotating screw or the reverse, it being understood that theball screw system that generates a movement of translation from arotational movement can be replaced by a cam system or even a crankshaftor equivalent device.

Through the above arrangement it is possible to determine the positionof the trigger and thus the order issued by the user, as well as theposition of the movable active element that activates the blade. Knowingthese two positions permanently and precisely, the blade position can belinked to that of the trigger by means of the electronic boardcontrolling the gear motor, and that of the movable active element thatactivates said blade.

More generally, the invention includes an original arrangement ofportable electric tools, in particular electric or electronic pruningshears, according to which particular devices, although known per se,have been adopted to determine the relative position among cooperatingelements essential to those apparatuses, constituted, respectively, bythe actuator of the movable blade thereof and by the trigger of thecontrol device of this actuator, these devices being controlled by anelectronic actuator control board capable of linking movements of theblade to that of the trigger.

The electric pruning shears or similar cutting tool according to theinvention also provides other interesting advantages. For example:

it does not have moving electronic components, which provides improvedoperating reliability;

the distance between the components of the detection device(oriented-magnetization magnet and magneto-resistive sensor) can beshort, which avoids the need to use powerful magnets and allows forreduced tool volume;

there is no contact between the components of the detection device and,consequently, no wear of these latter;

it does not require the use of powerful magnets; and

it provides a direct reading of the position of the actuator based onthe inclination of the magnetic field lines of the magnets; therefore,it is not necessary to perform calculations to determine this position.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objectives, characteristics, and advantages, as well asothers, can be better understood from the following description andattached drawings, in which:

FIG. 1 is a schematic view of a first known detection device that can beused in a system for determining the position of a movable part.

FIG. 2 is a schematic view of another known detection device.

FIG. 3 is a schematic view of a first embodiment of another knowndetection method, applicable to a system that can be used to determinethe position of a linearly moving movable part.

FIG. 4 is a schematic view of a second embodiment of the detectionmethod illustrated in FIG. 3, applicable to a system that can be used todetermine the position of an angularly moving movable part.

FIG. 5 is an elevation view, with partial cutaways, of an electricpruning shears according to the invention.

FIG. 6 is a very simplified elevation view of the pruning shears.

FIG. 7 is an isolated view of FIG. 6 at a greater scale showing theprincipal components of the pruning shears described by the invention,the movable blade thereof being mounted in completely open position.

FIG. 8 is an isolated view similar to FIG. 7 and showing the movableblade in partially open position (semi-open).

FIG. 9 is an isolated view similar to FIGS. 7 and 8 and showing themovable blade in closed position.

DETAILED DESCRIPTION OF THE INVENTION

Reference is made to said drawings in describing an interesting,although not limiting, embodiment of a portable electric tool accordingto the invention, which, according to this advantageous example,comprises electric pruning shears.

The drawings shown in FIGS. 3 and 4 illustrate two embodiments of themethod for determining the relative position between two cooperatingparts at least one of which is movable, wherein electromagneticmechanisms ensure the operation of portable electric tools according tothe invention.

According to this method, which is known per se, said movable part ismade integral with oriented-magnetization magnet A, that is, a magnetwhose magnetic field lines are angled inversely starting from the centerthereof, this oriented-magnetization magnet being moved before amagneto-resistive sensor C affixed to a fixed part 1 c.

According to the embodiment shown in the drawing of FIG. 3, magnet A issupposed to be affixed to a linearly moving movable part.

The solid line and dashed line illustrate the two extreme positions ofthe oriented-magnetization magnet A with respect to themagneto-resistive sensor C.

According to a second embodiment illustrated by the operating diagram ofFIG. 4, a curved oriented-magnetization magnet A′ is affixed to acylindrical part P that moves angularly. In this drawing, threepositions of oriented-magnetization magnet A′ are shown with respect tomagneto-resistive sensor C:

on the left side of the figure, magnet A′ is shown in a centralposition;

the central portion of the figure shows a counterclockwise angularmovement of part P and magnet A′;

whereas on the right of the figure, magnet A′ is shown after a clockwisemovement.

In the three positions, and in every intermediate position comprisedbetween the extreme positions thereof, the magnetic field lines oforiented-magnetization magnet A′ are detected by magneto-resistivesensor C.

It is also known that the magnetic field lines of magnet A′ aregradually inclined in proportion to their distance from the center ofsaid magnet, for example, 1° for 1 mm, then 2° for 2 mm, and so on.

By using a magneto-resistive sensor that can determine the degree ofinclination of the magnet's magnetic field lines, it is possible todeduce the angular value of the magnet's travel and, consequently, ofpart P (1 mm for 1°, according to the above example).

This deduction and the management of the measured travel are performedby an electronic control board that comprises a microprocessor and thatreceives the signals issued by sensor C.

The invention relates to a portable electric tool having a body 1 shapedto serve as a handgrip and at one of whose extremities is mounted amovable active element 2 whose movements are engendered by an actuator 8and a control device 6 capable of controlling the operation of saidactuator via an electronic command and control board. This portableelectric tool is notably remarkable in that said actuator 8 makes use ofthe device for determining the relative position between two parts, atleast one of which is movable, the motion thereof being linear orangular as previously described; and/or in that control device 6 makesuse of this device for determining the relative position between one ofthose parts, at least one of which is movable.

Below we describe a very advantageous application of the invention toelectric or electronic pruning shears. It should be borne in mind,however, that it can also be applied to other portable electric toolswith cutting blades, such as garden shears.

Electric or electronic pruning shears generally comprise a hollow body 1shaped to serve as a handgrip and at the anterior extremity of which ismounted a cutting head having at least one movable active element 2.Generally, this active element consists of a pivoting cutting blademounted on a counterblade or fixed hook 3 by means of an axis ofarticulation 4. Within body 1 is lodged a gear motor 5 whose output isconnected to said movable active element 2 by means of a transmissionsystem. These electric or electronic pruning shears further have acontrol device having a trigger 6 mounted with the ability to pivotabout an axis 7 and accessible on the exterior of body 1.

According to an advantageous embodiment, the transmission systemconnecting the output of gear motor 5 to movable blade 2 comprises amovable drive part including ball 8 of a ballscrew system 8-9 and a pairof rods 10.

Rotating screw 9 is coupled to the output of gear motor 5, while axiallymovable ball 8 is connected, by means of pair of rods 10 andarticulations, to an extension or lever 2 a presented by pivoting blade2.

More specifically, rods 10, by means of articulations 11 and 12, arecoupled, respectively, to extension 2 a of pivoting blade 2 and to ballbody 8 constituting the tool's actuator. In this way any linear movementof the latter brings about, by means of rods 10, a pivoting movement ofmovable blade 2 around axis 4, closing and opening said blade withrespect to the fixed blade or hook 3.

According to a characteristic arrangement, the portable electric toolhas:

on the hand, a magnet with oriented magnetic field lines 13 fixedlymounted on movable ball 8 and a magneto-resistive sensor 14 fixedlymounted to body 1 at a location before which said oriented-magnetizationmagnet 13 travels during the forward and backward linear movements ofsaid ball 8; and

on the other hand, a magnet with oriented magnetic field lines 15affixed to trigger 6, preferably on the free extremity thereof and, inan element 1 a of body 1, or on an element integral with the body, amagneto-resistive sensor 16 is fixedly mounted, at a location beforewhich moves said oriented-magnetization magnet 15 equipping the freeextremity of pivoting trigger 6 during pivoting movements thereof.

Advantageously, magneto-resistive sensor 16 is fixedly mounted in aconnecting part 1 a rigidly connecting body 1 and the tool's protectiveguard 1 b, which has the benefit of strengthening this guard and makinguse of the tool more comfortable, especially to prevent it fromrecoiling in the hand when working at a height.

The signals issued by magneto-resistive sensor 14 are transmitted to anelectronic control board (not shown) configured and programmed tocontrol gear motor 5 and thus control the opening or closing of movableblade 2 and also the stopping of said blade in any intermediate positionbetween closed and fully open.

The signals issued by magneto-resistive sensor 16 are transmitted to anelectronic control board (not shown) configured and programmed tocontrol gear motor 5; this electronic control board can be the same asthat which receives the signals issued by magneto-resistive sensor 14.

More specifically, this electronic control and management boardcomprising a microprocessor is configured to analyze the analog ordigital electrical information transmitted by each magneto-resistivesensor 14, 16, depending on the inclination of the magnetic field linespresented to it, to control the operation of actuator 8 in order toprecisely position movable element 2 based on the position of controldevice 6.

It is understood that the invention can be applied to the control systemof actuator 8 of pivoting blade 2 (oriented-magnetization magnet 13 andmagneto-resistive sensor 14) to determine and control the openingthereof as well as to the control system comprising trigger 6(oriented-magnetization magnet 15 and magneto-resistive sensor 16) todetermine the travel of said control trigger.

It is further understood that when trigger 6 and, thus, associatedoriented-magnetization magnet 15 is moved by a certain angle (the valueof the movement of blade 2 desired by the user), magneto-resistivesensor 16 reads an angle of inclination of the magnetic field of saidmagnet 15 corresponding to the angular displacement of said trigger 6.

This value read by magneto-resistive sensor 16 is transmitted to theelectronic command and control board of gear motor 5, which gives theorder to said motor to set itself in motion and thereby actuate, in thedesired direction, the ballbearing ballscrew device 8-9, in order tomove blade 2 by means of rods 10.

When ball 8 moves to realize this action, oriented-magnetization magnet13, which is affixed to said ball, moves in front of magneto-resistivesensor 14 affixed to body 1 of the tool.

When magneto-resistive sensor 14 reads an angle of inclination of themagnetic field of oriented-magnetization magnet 13 corresponding to themovement controlled by the electronic control board, the latterimmediately stops gear motor 5.

It can be seen that, in this manner, it is possible to precisely controlthe position of blade 2 during opening and closing and, therefore, toprecisely link it to the position of the trigger controlled by the user.

In short, the invention includes integrating, at determinate locationsof portable electric tools such as electric or electronic pruningshears, particular devices for determining the relative position betweencooperating elements essential to such devices, constituted,respectively, by the actuator of the movable blade thereof and by thetrigger of the control device of said actuator, these devices beingmanaged by an electronic board capable of very precisely linkingmovements of the blade to that of the trigger.

Obviously, it would be possible, for the trigger and with respect topruning shears whose blade is actuated directly by a rotating andnonlinear device (for example, pruning shears of the type described inFR-2670372, WO-2005/084416), to apply the constructive solutiondescribed to angular movements as illustrated in FIG. 4.

I claim:
 1. A. portable electric cutting tool comprising: a body havinga handgrip and baying a movable active element at one end thereof; anactuator positioned in said body, said actuator having a pair ofcooperating parts, one of said pair of cooperating parts being movablelinearly or angularly so as to move said active element of said body; acontrol device cooperative with said actuator so as to control anoperation of said actuator, said control device baying a pair ofcooperating parts, one of said pair of cooperating parts of saidactuator having a magnet with a magnetization oriented in a directionand another of said pair of cooperating pans of said actuator having amagneto-resistive sensor, one of said pair of cooperating parts of saidcontrol device having a magnet with a magnetization oriented in adirection and another of said pair of cooperating parts of said controldevice having a magneto-resistive sensor; and an electronic controlboard having a microprocessor, said electronic control board configuredsuch that analog or digital electrical information transmitted by themagneto-resistive sensors can be analyzed based on an inclination ofmagnetic field lines to the magneto-resistive sensors, said electroniccontrol board for controlling said actuator for positioning said movableelement based on a position of said control device.
 2. The portableelectric cutting tool of claim 1, said magnet of said one of said pairof cooperating parts of said actuator movable forward of saidmagneto-resistive sensors of said actuator.
 3. The portable electriccutting tool of claim 1, said control device comprising: a trigger forcontrolling the operation of said actuator by said electronic controlboard, said magnet of said control device affixed to a stationaryelement integral with said body, said magnet of said trigger positionedforward of said magneto-resistive sensor of said stationary element. 4.The portable electric cutting tool of claim 1, said control devicecomprising: an electric gear motor housed within said body, saidelectric gear motor having an output connected to said movable activeelement of a transmission system; and a pivotable trigger cooperativewith said electronic control board, said trigger having a free end, saidmagnet of said control device mounted to said free end of said trigger,said magneto-resistive sensors of said control device fixedly mountedonto an element integral to said body.
 5. The portable electric cuttingtool of claim 1, said actuator having a movable ball of a ballbearingballscrew system, said magnet of said actuator affixed to said movableball, said magnet of said actuator being movable by activation of saidballbearing ballscrew system, said magneto-resistive sensors of saidactuator fixedly mounted to said body.